PFCs gases, which are much used in semiconductor and display manufacturing processes, are greenhouse gases causing global warming and have a higher global warming potential by several thousands to tens of thousands of times than CO2. Accordingly, the PFCs gases should be emitted to the air through treatment equipment.
Generally, various kinds of reaction gases used to form a thin film on a wafer or to etch the thin film in the semiconductor manufacturing process have the properties of explosion, extremely high toxicity and suffocating, and accordingly, if they are emitted to the air with no treatment, they are harmful to the human bodies and cause global warming and environmental pollution. Therefore, a scrubber as a gas purification system is provided in the exhaust line of semiconductor equipment to decompose and remove the refractory hazardous gases and to exhaust the purified gases to the air. The refractory hazardous gases are diluted with nitrogen (N2) as an operating fluid of a vacuum pump used to maintain a negative pressure in the process and thus have a density of several hundreds to thousands of ppm or under. After the dilution, the gases are introduced into the scrubber. Hereinafter, the refractory hazardous gases diluted with the inert gas are defined as waste gases.
As known, refractory gases, PFCs are decomposed at a temperature of more than 1600° C., SF6 at a temperature of more than 1200° C., and NF3 at temperature of more than 800° C.
The PFCs, SF6, and NF3 are decomposed to the bonded forms to fluorine and exhausted to the forms of hydrofluoric acid and fluorine, and in this case, they have the properties of extremely high toxicity and explosion, so that they have cleaning reaction with water and are then exhausted.CF4(g)+O2(g)→CO2(g)+2F2(g)SF6(g)+O2(g)→sO2(g)+3F2(g)2NF3(g)+O2(g)→2NO+3F2(g)2F2+2H2O(g)→4HF+O2 
The F2 decomposed through oxidation reaction is reacted generally with water or H2O as a product after burning and exhausted to the form of HF(g) or HF(l).
The scrubber, which removes semiconductor waste gases generated in the semiconductor manufacturing process, is largely classified into three kinds of scrubbers, that is, an indirect oxidation wet scrubber, a wet scrubber, and a direct burning wet scrubber. Firstly, the indirect oxidation wet scrubber is configured to oxidize waste gases by means of induction heating or electric heater and to treat the particles or soluble gases produced after the oxidation by means of post process using water. Secondly, the indirect oxidation wet scrubber is called a heat-wet scrubber. The wet scrubber is configured to treat the soluble gases contained in waste gases with water and then to exhaust the treated soluble gases. Thirdly, the direct burning wet scrubber is configured to burn waste gases by means of natural gas or propane gas and then to collect soluble gases or particles through water.
As the semiconductor waste gases, further, gases (SiF4, SiH4 and the like) containing silicon and PFCs gases are at the same time introduced in large quantities. In this case, if the heat-wet scrubber or the burn-wet scrubber is adopted, a large quantity of powder is produced in the interior of the scrubber. An example of chemical formula producing powder is as follows.SiH4 (gas)+2O2→SiO2 (powder)+2H2O
As time passes, by the way, the powder produced after the semiconductor waste gases are burned becomes thickly and more rigidly settled on the inner wall of a burning chamber by means of attractive force and frictional force.
As examples of the waste gas treatments through the scrubber, at present, there are burning, catalytic decomposition, thermal plasma burning, and electrolysis.
Firstly, the burning treatment is conducted by using fossil fuels (for example, LNG) and has some disadvantages of low treatment efficiencies of PFCs, bad flame stability (burning process) and the decrement of products (for example, NOx and CO) after burning.
Secondly, the catalytic decomposition treatment has some problems of catalyst poisoning by high density acid gas (HF, HCL, etc.), increment of operating cost due to short catalyst exchange period, and pressure rise of a system caused by the introduction of particles.
Lastly, the thermal plasma burning and electrolysis treatments make use of electricity as an energy source, and accordingly, they need very high power energy when compared with the capacity treated. The thermal plasma burning treatment causes frequent exchange due to the non-existence of durable torch materials, generates a large quantity of NOx, and needs the bulkiness of incidental equipment (transformer) according to power increment upon high capacity treatment. Further, the electrolysis treatment has a short exchange period due to the durability problem (electric heater etching) of a heating element and is hard to conduct heating at a high temperature of more than 1600° C.
FIG. 1 is a front view showing a conventional waste gas treatment scrubber system. As shown in FIG. 1, the scrubber system 1 for treating semiconductor waste gases includes a plurality of waste gas inlets 112 connected to semiconductor manufacturing process lines, a burner 5 connected to the waste gas inlets 112, a combustion device 110 coupled to the burner 5, a water storage tank 4 coupled to the lower end of the combustion device 110 to collect the powder generated from the combustion device 110 and then to settle the power in water, and a wet tower 3 coupled to the combustion device 110 and the water storage tank 4 to treat fine powder and soluble gases passing through the combustion device 110 with water. In this case, the combustion device 110 and the wet tower 3 may be connected to each other by means of a separate connection pipe, and further, the wet tower 3 has an exhaust pipe formed on the top portion thereof.
According to the conventional scrubber system 1 for treating the semiconductor waste gases, various kinds of waste gases are supplied from the semiconductor manufacturing process lines through the waste gas inlets 112. The waste gases supplied through the waste gas inlets 112 are supplied to the combustion device 110 through the burner 5. The waste gases supplied to the interior of the combustion device 110 are burned by means of the burner 5, and through the combustion, large quantities of hydrofluoric acids, fluorine, and powder are produced. Relatively heavy powder of the produced powder drops by gravity, and then, the powder is settled in the water of the water storage tank 4. On the other hand, relatively light fine powder, which does not drop to the water storage tank 4, is moved to the wet tower 3 through the connection pipe connected between the combustion device 110 and the wet tower 3. The fine powder moved to the wet tower 3 is collected again by means of water, and the collected fine powder drops again to the water storage tank 4 so that it is settled in the water. Of course, the waste gases purified through the wet tower 3 are exhausted to the air through the exhaust pipe.
So as to burn the waste gases, like this, the waste gases should be oxidized at a high temperature more than 1,600° C. (CF4), and as mentioned above, waste gases, that is, refractory hazardous gases are diluted with inert gas (generally, N2) of more than 99% and injected and burned into the scrubber system 1. In this case, however, even the inert gas whose treatment is unnecessary should be heated, thus undesirably making the treatment efficiencies and energy efficiencies substantially lowered.
According to the conventional practice, as shown in FIG. 1, fuel and oxidizer (oxygen) are supplied to the combustion device 110 from fuel inlets 111 and oxidizer inlets 113 through nozzles attached to the combustion device 110 inside the scrubber system 1. Next, the fuel and oxidizer are ignited to form nozzle-attached flames, and the waste gases are injected into the combustion device 110 through the separated waste gas inlets 112.
FIG. 2 is a schematic view showing waste gases and flames generating swirl flows in the conventional practice. Further, FIG. 3 is a schematic view showing flames injected in a cross-flow way with respect to the flows of waste gases in the conventional practice, and FIG. 4 is a photograph showing the flames of FIG. 3.
The waste gases injected into the combustion device 110 are heated and oxidized, while flowing in parallel with the flames or slantly against flames. If the longitudinal directions of the flames determined by the injection angles of the fuel and oxidizer nozzles are parallel with the flow directions of the waste gases, as shown in FIG. 2, the mixing between the high temperature flames and the waste gases becomes slow, and so as to facilitate the mixing, accordingly, swirls are generated (mixing enhancement way). Otherwise, as shown in FIGS. 3 and 4, the injection directions of the fuel and oxidizer nozzles cross the flow directions of the waste gases (cross-flow way) so that the waste gases can hit the high temperature flames and go out of the flames.
Even if the swirls are sufficiently generated in FIG. 2, however, it is difficult that the combustion gases and the waste gases are sufficiently mixed with each other in the combustion device 110 whose size is restricted. Generally, flow rates of waste gases are higher than that of combustion gases, so that large momentums of the waste gases make the flames unstable or even extinguished, thus undesirably decreasing the treatment efficiencies. So as to form the stable flames and enhance the treatment efficiencies, at this time, there is a need to additionally use the fuel and oxidizer. In this case, however, energy efficiencies become low.
Further, as shown in FIGS. 3 and 4, the flames 2 having the shapes of inverted slant cones become not closed on the slant surfaces thereof, but become open by means of the momentums of the waste gases, so that the waste gases are escaped from the high temperature flames, thus undesirably decreasing the decomposition efficiencies.